The present invention relates to a conveying system, and in particular to a mechanism for feeding articles into a stack and removing articles from a stack.
Stacker/unstacker systems are presently available, one such system being disclosed in U.S. Pat. No. 3,933,254, issued Jan. 20, 1976 to W. C. Pulver et al., and assigned to the assignee of the present invention. The Pulver et al. stacker/unstacker is typical of prior art systems in that it is designed to add articles to a stack or remove articles from a stack at a fixed position at a predetermined elevation. In such systems, it is necessary to move the entire stack up and down during the stacking and unstacking operation to maintain the top of the stack at the fixed position. In the case of bread pans and the like, which are typically formed of fairly heavy gauge ferromagnetic materials and which are typically strapped together in straps of up to six pans, a stack of such pan straps can be quite heavy, often weighing in excess of one thousand pounds per stack. The accurate positioning of such a stack in the prior art systems requires extremely heavy-duty and rugged equipment, and the weight of the stacks severely limits the attainable rates of operation.
Furthermore, the prior art stacker/unstacker systems typically include some sort of a conveying system for carrying the receptacles to and from the fixed transfer position at the top of the stack. Because the transfer position is fixed, this conveying necessarily requires an intermittent or reciprocating movement. In the Pulver et al. system, the receptacles are more or less continuously conveyed to a position overlying the top of the stack, and the reciprocating movement is the movement of a magnetic device for vertically shifting the receptacles one at a time between the transfer conveyor and the stack. Such intermittent or reciprocating mechanical movements are necessarily complicated, cumbersome and subject to more frequent breakdown and maintenance expenses than are continuous movement systems.
The design of the prior art stacker/unstacker systems is such that they are necessarily tailored to handling particular types of articles, the systems not being readily adaptable to the handling of other types of articles. Furthermore, the stacks can only be formed on the stacker/unstacker machine itself and, more particularly, on the sack elevator apparatus thereof, thereby greatly limiting the flexibility of the prior art systems.